the Ashing Technique Microdetermination of Metals by

CHAPTER 6

Microdetermination of Metals by the Ashing Technique

A number of metals* in organic compounds may be determined by a simple ashing procedure with or without the addition of sulfuric or nitric a c i d s .

However, only one metal may be present in the com­

pound, or this method is not applicable and determination must be accomplished by adapting one of the macromethods found throughout the l i t e r a t u r e .

'

Before attempting to determine any metal by this method, the reader should consult the l i t e r a t u r e

to make certain in which state the metal would be present at the end, namely, the oxide, sulfate, or free metal, and if these would or would not be lost by volatilization at the temperature involved. The method is not applicable to compounds containing phosphorus, since this is not completely driven o f f .

The substance is treated with sulfuric acidf and placed in a muffle in which the acid is driven off and the residue heated at red heat.

The reactions may be represented by the following, depending upon the metal involved.

—Na N a²S 0⁴

— Κ , k²s o⁴

—Ca H0S 04 C AS° 4

— B a B a S 0⁴

etc. etc.

- A g Ag

—Au > Au

—Pt Pt

—Cu CuO

—Fe ( H N 0²) F e²0³ ( H²S 0⁴)

etc. etc.

* Determination of arsenic is carried out according to the method given in Chapter 13.

f Sulfuric acid is added in cases where the sulfate is stable at red heat. For silver, gold and platinum, no acid need be added. Where the oxide will be formed at the end of the determination, nitric acid may be added, as for example with copper, iron, etc.

Silver may exist as sulfate or chloride in which case the factor would not be 1.000.

133

Reagents

DILUTED SULFURIC ACID

1 part cone. H

S 0

(sp. gr. 1.84) 5 parts distilled water.

DILUTED NITRIC ACID

1 part cone. H N 0

(sp. gr. 1.42) 1 part distilled water.

Apparatus

PLATINUM BOAT

The platinum boat required is the standard i t e m

'

-

described in Chapter 3, Fig. 24.

PLATINUM CYLINDER

The platinum cylinder

-

shown in Fig. 8 4 is used as a sleeve into which the platinum boat is placed. I f spattering occurs during the determination the

material is deposited on the inner surface of the cylinder, preventing loss. It is made of platinum foil approximately 0.04 mm. thick, is about 3 cm. long

η Λ ~Λ ~ * A i i and has a diameter of approximately 7.5 mm. T o

FIG. 84. The Coombs-Alber , , ^Γ ,

platinum cylinder (sleeve).

cylinder is attached a piece of thin platmum wire, the end of which is shaped into a hook.

This is used in pushing the cylinder into the micromuffle and pulling it out.

MICROMUFFLE

The micromuffle consists of a tube (Pyrex 1 7 2 0 glass,* Vycor,* or quartz) which is heated to 6 8 0 ° - 7 0 0 ° C. and through which passes a slow current of air. Although the original micromuffle of P r e g l

'

-

'

'

-

'

-

-

was gas heated, the author prefers e l e c t r i c

-

-

units as these provide more constant heat, with equal distribution. This helps to prevent creeping of the material during the early stages of the heating and insures more constant ashing conditions.

The apparatus used by the author is shown in Figs. 85 and 86. It is a double unit which permits two determinations to be carried out simultane­

ously. It consists of two sections of combustion tubing about 225 mm. in length, one tube for each determination. These are portions of standard combustion tubing, Pyrex 1720 glass,* Vycor,* or quartz, approximately 11 mm. O.D. and 8 mm. I.D. [ a section of the tube shown in Fig. 9 8 (Chapter 7 ) or Fig. 121

* Corning Glass Works, Corning, New York.

135 Apparatus

(Chapter 9 ) ] . The tubes are fastened in a support and pass through the two holes of the movable electric burner* or furnace. At one end, each tube is open and at the other end it is attached to a small bubble counterf which con­

tains about 1 ml. of concentrated H

S 0

so that the rate of flow of air through

FIG. 8 5 . Micromuffle.

U - T U B E

COMBUSTION FURNACE COMBUSTION (NICHROME WINDINGS

T U B E OVER I REFRACTORY TUBE)

SIDE VIEW

FIG. 8 6 . Micromuffle—details of construction.

the tubes may be observed. The opposite end of the bubble counter is attached to a filter tube containing cotton, which in turn is connected to a compressed air supply.

The movable electric furnace is made from windings of small nichrome

* See footnote p. 154, Chapter 7.

f Portion of a broken bubble counter-U-tube (Chapter 9 ) may be used.

wire wound around two sections of alundum tubing approximately 1 3 - 1 4 mm. I.D. and about 65 mm. in length. The temperature is controlled to 6 8 0 ° - 7 0 0 ° C. by operating the furnace from a variable auto-transformer. The furnace is attached to a worm drive which is powered by a small electric clock motor,

making the drive automatic with a forward speed of approximately 2.5 cm. in 10 minutes.

In many respects, the micromuffle is quite similar to that described by A. R.

Norton, G. L. Royer, and R. K o e g e l .

Procedure

The boat and cylinder are cleaned by immersion in hot dilute nitric acid, washed with distilled water, strongly ignited in the flame of a gas burner, and set in a microdesiccator (Chapter 3, Figs. 4 3 - 4 6 ) to cool. The dismantled combination is then accurately weighed on the microchemical balance (taking into account the zero reading). About 5 mg. of sample is added to the boat and the combination reweighed. (Note: I f the sample is hygroscopic, the weighing pig is used to protect the sample as described in Chapter 3—see Figs. 29, 30, and 3 2 ) . Three drops of the diluted sulfuric acid* are care­

fully added to the sample and the boat is then placed in the cylinder using a platinum-tipped forceps (Chapter 3, Fig. 4 1 ) to hold each piece during the manipulation. The combination is then placed in the open end of the combustion tubing and pushed far enough in so that all portions, including the wire hook, will be heated eventually. Care should be taken so that the boat is kept upright during the placing. The passage of air through the bubble counter is regulated so that bubbles pass through at the rate of about 1-2 per second. The furnace is placed back so that it is about at the one end of the cylinder opposite to the opening (about 5 - 6 cm. from the open end of the combustion tube). It is then switched on and the temperature brought up to 6 8 0 ° - 7 0 0 ° C. The mechanical drive is set into motion and the hot furnace is passed over the entire length of the cylinder and is allowed to remain in the end position (over the cylinder) for about 1 5 - 2 0 minutes. The combination is then carefully removed from the micromuffle and allowed to cool in a microdesiccator after which it is weighed to obtain the weight of the ash (taking into account the zero reading). It is good practice to reheat the combination in the micromuffle for 5 minutes and reweigh. This insures that constant weight has been attained.

Calculation:

Wt. ash X factor X 100

% Metal

W t . sample See f, Ρ- 133.

137 Additional Information for Chapter 6

Factors:*

Ash Element sought Factor

N a²S 0⁴ Na 0 . 3 2 3 7

K2S O4 Κ 0 . 4 4 8 7

B a S 0⁴ Ba 0 . 5 8 8 5

C a S 0⁴ Ca 0 . 2 9 4 4

CuO Cu 0 . 7 9 8 8

F e²O^s Fe 0 . 6 9 9 4

Pt Pt 1 . 0 0 0

Au Au 1 . 0 0 0

Ag Ag ^{1 . 0 0 0}

Examples:

( a ) 5.632 mg. of ash ( N a²S 0⁴) is obtained from a 7.631-mg. sample 5.632 X 0.3237 X 100

= 2 3 . 8 9 % Na 7.631

( b ) 2.610 mg. of ash ( C u O ) is obtained from a 8.001-mg. sample 2.610 X 0.7988 X 100

= 2 6 . 0 6 % Cu 8.001

( c ) 1.074 mg. of ash ( A g ) is obtained from a 7.016-mg. sample

1.074 χ 1 X 100 ^ ^A

Λ = " . 3 1 %

Ag

ADDITIONAL INFORMATION FOR CHAPTER 6

The micromuffle used by P r e g l

-

'

-

'

-

'

-

-

is shown in Fig. 8 7 . It consists of a right angle tube and a straight one. The vertical portion of the right angle is heated to supply a hot air current.

Norton, Royer, and K o e g e l

described an automatic electric microfurnace.

It provides for the ashing of two samples simultaneously. The two quartz com­

bustion tubes are drawn through the furnace in contrast to that shown in Figs.

8 5 and 8 6 in which the tubes are stationary and the furnace moves along. The

above authors used a standard two-speed governor controlled phonograph motor geared so that the rate of travel is approximately either 1 or 2 inches

( 2 . 5 or 5 cm.) in 1 0 minutes. Platinum heating coils are used. The voltage

to these is controlled by means of a variable auto-transformer. The furnace is operated at a temperature of 8 0 0 ° C .

* Only a few typical factors are given here. For other cases, the reader is referred to the various handbooks containing gravimetric f a c t o r s .5 9-1 0 7'1 0 8 Also see Chapter 23.

Also see footnote on page 133.

FIG. 87. Pregl micromuffle.

T A B L E 16

ADDITIONAL INFORMATION ON R E F E R E N C E S * R E L A T E D TO C H A P T E R 6

Although this chapter deals with the determination of metals by the ashing technique, the author wishes to present additional information in the form of a table as in the preceding chapters. (See author's statement at top of Table 4 of Chapter 1.) The refer­

ences listed in this table refer to the determination of metals by other means as well as the determination of several amphoteric elements not covered in detail in other chapters.

Books

Belcher and Godbert, 17, 18 Clark, E. P., 59

Clark, S. J . , 60

Fritz and Hammond, 81 Furman, 82

Grant, 90, 91

Milton and Waters, 167, 168 Niederl and Niederl, 171, 172 Niederl and Sozzi, 173 Pregl, 184

Roth, 195-198 Steyermark, 223

General, miscellaneous

Belcher, Gibbons, and Sykes, 16 Belcher, Macdonald, and West, 19 Cimerman and Selzer, 54, 55

General, miscellaneous (Conf.)

Martin, 158

Meyrowitz, and Massoni, 166 Norton, Royer, and Koegel, 176 Sykes, 231

Van Etten and Wiele, 239

Reviews

Belcher, Gibbons, and Sykes, 16 Sykes, 231

Apparatus

Norton, Royer, and Koegel, 176

Bombs

Kondo, 134 Kuck and Grim, 142

* The numbers which appear after each entry in this table refer to the literature citations in the reference list at the end of the chapter.

139 Table of References

T A B L E 16 (Continued) Perchloric acid

Smith, 217

Oxygen flask combustion Belcher, Macdonald, and West, 19 Corner, 62

Southworth, Hodecker, and Fleischer, 221 Kjeldahl flask digestion

Kreshkov, Syavtsillo, and Shemyaten- kova, 141

Simultaneous determinations Klimova and Bereznitskaya, 129, 130 Klimova, Korshun, and Bereznit-

skaya, 131, 132

Korshun and Chumachenko, 137 General volumetric methods

Belcher and Robinson, 20 Belcher and West, 21 Cimerman and Ariel, 4 8 - 5 0 Cimerman and Bogin, 51 Cimerman and Frenkel, 52 Cimerman and Selzer, 54 Deibner, 65

Gautier and Pellerin, 83

Gusev, Kumov, and Stroganova, 93 Kuck and Grim, 142

Schulitz, 210

Sloviter, McNabb, and Wagner, 215 Strahm and Hawthorne, 226 Sudo, Shimoe, and Miyahara, 230 Venkateswarlu, Ramanthan, and

Narayana Rao, 240 Zabrodina and Bagreeva, 248 Heterometric titration

Bobtelsky and Eisenstadter, 24 Bobtelsky and Graus, 25, 26 Bobtelsky and Hapern, 27 Bobtelsky and Jungreis, 2 8 - 3 2 Bobtelsky and Rafailoff, 33, 34 Bobtelsky and Welwart, 35-38 Complexometric, EDTA titration

Amin, 6

Ashby and Roberts, 10

Complexometric, EDTA titration (Conf.) Flaschka, 7 4 - 7 7

Flaschka and Amin, 78 Flaschka, Amin, and Zaki, 79 Harrison and Harrison, 96 Karrman and Borgstrom, 121 Kimbel, 122

Kinnunen and Merikanto, 125 Parry, 179

Socolar and Salach, 219 Southworth, Hodecker, and

Fleischer, 221

Flame photometric. X-ray spectropho- tometry, colorimetric, etc., methods

Almassy and Kavai, 4 Arnold and Pray, 9 Asperger and Murati, 11 Barrett, 14

Beauchene, Berneking, Schrenk, Mitchell, and Silker, 15

Buell, 41

Chatagnon and Chatagnon, 47 Gautier and Pellerin, 83 Gillam, 88

Grogan, Cahnmann, and Lethco, 92 Hegediis, Fukker, and Dvorszky, 99 Hunter, 112

Ikeda, 114

Ishibashi and Higashi, 115 Kingsley and Schafïert, 124 Kozawa, Tanaka and Sasaki, 139 Kreisky, 140

Lapin and Makarova, 148 Leonard, Sellers, and Swim, 149 Leroux, Mafïett, and Monkman, 150 Lewis, 151

Lindstrom, 153 Lipscomb, 154 Marier and Boulet, 157 Martin, 159, 160 Mehlig, 163

Natelson and Penniall, 170 Nonowa, 175

Nozaki, 177

Polley and Miller, 183 Sakuraba, 201

T A B L E 16 (Continued) Flame photometric, X-ray spectropho­

tometry, colorimetric, etc., methods (Conf.)

Saltzman, 202 Schuhknecht, 206

Schuhknecht and Schinkel, 207 Schultz, 211

Solomon, 220 Teeri, 232

Toribara and Sherman, 234 Tunnicliffe, 236

Tutundzic and Mladenovic, 237 Umland and Weyer, 238 Zuehlke and Ballard, 250

Potentiometric, polarographic, etc., methods

Carruthers, 45 De Francesco, 64 Heyrovsky, 103 Jensen, 116

Kadowaki, Okamoto, and Nakajima, 118 Kuck and Grim, 142

Lambert and Walker, 145 Well, 243

Manometric methods See Chapter 18 Hoagland, 106

Gravimetric methods, precipitation, etc.

Barber and Kolthoff, 13 Cimerman and Selzer, 55 Fennel and Webb, 73

Gusev, Kumov, and Stroganova, 93 Kondo, 134

Walton and Smith, 242 Electrodeposition

Llacer, Sozzi and Benedetti-Pichler, 155 Chromatographic methods

Lacourt, 144 Lamm, 146

Radioactive methods Korenman, Sheyanova, and

Glazunova, 136

Antimony

Bahr, Bieling, and Thiele, 12 Gellhorn, Krahl, and Fertig, 85 Haight, 94

Jurecek and Jenik, 117 Schulek and Wolstadt, 209 Silvert and Kirner, 214 Arsenic

See Chapter 13 Barium

Pungor and Hegedus, 186 Pungor and Thege, 187 Beryllium

Toribara and Sherman, 234 Bismuth

Silvert and Kirner, 214 Boron

Allen and Tannenbaum, 3 Belcher, Macdonald, and West, 19 Buell, 41

Corner, 62

Gautier and Pignard, 84 Kuck and Grim, 142 Martin, 160

Pflaum and Wenske, 181 Roth, 194

Strahm and Hawthorne, 226 Cadmium

Cimerman and Selzer, 54 Furman, 82

Saltzman, 202 Steyermark, 223 Calcium

Andersch, 7

Ashby and Roberts, 10 Bobtelsky and Eisenstadter, 24 Gilbert, 86, 87

Harrison and Raymond, 95 Harrison and Harrison, 96 Herrmann, 102

Hunter, 112, 113

141 Table of References

T A B L E 16 (Continued)

Calcium (Conf.)

Ikeda, 114 Kimbel, 122

Kingsley and Schaffert, 123, 124 Kirk and Tompkins, 127 Lindner and Kirk, 152 Marier and Boulet, 157 McGregor, 161

Natelson and Penniall, 170 Nonowa, 175

Patel, 180

Pungor and Hegediis, 186 Pungor and Thege, 187 Rappaport and Rappaport, 189 Scholtis, 205

Schuhknecht, 206 Schultz, 211

Socolar and Salach, 219 Steyermark, 223 Teeri, 232 Wilkinson, 246

Chromium

Grogan, Cahnmann, and Lethco, 92 Kozawa, Tanaka, and Sasaki, 139 Lacourt, 144

Cobalt

Bobtelsky and Jungreis, 28 Cimerman and Selzer, 54 Ellis and Gibson, 70 Pohl and Demmel, 182 Sakuraba, 201 Saltzman, 203

Wenger, Cimerman, and Corbaz, 244

Copper

Amin, 6

Beauchene, Berneking, Schrenk, Mitchell, and Silker, 15

Benedetti-Pichler, 22 Bobtelsky and Graus, 26 Bobtelsky and Jungreis, 32 Bobtelsky and Welwart, 38 Carruthers, 45

Chatagnon and Chatagnon, 47 Dezsô and Fulôp, 66 Diehl and Smith, 67 Ellis and Gibson, 71

Copper (Conf.)

Emeléus and Haszeldine, 72 Furman, 82

Hecht and Reissner, 97 Hubbard and Spettelm, 111 Lapin and Makarova, 148

Llacer, Sozzi, and Benedetti-Pichler, 155 MacNevin and Bournique, 156 Mehlig, 163

Sakuraba, 201 Smith, 216 Steyermark, 223 Umland and Weyer, 238

Gold

Furman, 82

Konig, Crowell, and Benedetti- Pichler, 135

Onishi, 178 Steyermark, 223

Iron

Almassy and Kavai, 4 Belcher and West, 21 Bobtelsky and Jungreis, 29 Deibner, 65

Flaschka, 77 Furman, 82

Kirk and Bentley, 126 Knop and Kubelkova, 133 Nieuwenburg and Blumendal, 174 Rappaport and Hohenberg, 188 Steyermark, 223

Straub, 227

Tutundzic and Mladenovic, 237 Umland and Weyer, 238 Well, 243

Lead

Bobtelsky and Graus, 25 Bobtelsky and Rafailoff, 34 Brantner and Hecht, 40 Cimerman and Ariel, 4 8 - 5 0 Cimerman and Bogin, 51 De Francesco, 64 Furman, 82 Jensen, 116

Kuhn and Schretzmann, 143 Steyermark, 223

T A B L E 16 (Continued) Lithium

Hegedus and Dvorszky, 98 Nozaki, 177

Schuhknecht and Schinkel, 207 Steyermark, 223

Magnesium

Benedetti-Pichler and Schneider, 23 Bobtelsky and Welwart, 37 Butler, 43

Davidson, 63 Gillam, 88

Gusev, Kumov, and Stroganova, 93 Hoagland, 106

Hunter, 112, 113 Ikeda, 114

Karrman and Borgstrom, 121 Steyermark, 223

Strebinger and Reif, 229 Tunnicliffe, 236 Wilkinson, 246 Winkler, 247 Manganese

Flaschka, Amin, and Zaki, 79 Kozawa, Tanaka, and Sasaki, 139 Scott, 212

Mercury

Asperger and Murati, 11 Barrett, 14

Bobtelsky and Jungreis, 30, 31 Bobtelsky and Rafailoff, 33 Boëtius, 39

Cimerman and Frenkel, 52 Druzhinin and Kislitsin, 68 Emeléus and Haszeldine, 72 Furman, 82

Gautier and Pellerin, 83 Grant, 90, 91

Herd, 100 Hernler, 101

Hirai and Hayatsu, 105

Kadowaki, Okamoto, and Nakajima, 118 Korshun and Chumachenko, 137 Korshun and Lavrovskaya, 138 Leroux, Mafïett, and Monkman, 150 Lindstrom, 153

Mercury (Conf.) Lipscomb, 154

Meixner and Krocker, 164 Miura, 169

Parry, 179

Polley and Miller, 183 Rauscher, 190 Roth, F. J . , 193 Roth, H., 195-198 Rutgers, 199 Sachs, 200 Schulitz, 210

Shukis and Tallman, 213

Sloviter, McNabb, and Wagner, 215 Smith, 216

Southworth, Hodecker, and Fleischer, 221

Steyermark, 223

Sudo, Shimoe, and Miyahara, 230 Verdino, 241

Walton and Smith, 242 Zuehlke and Ballard, 250 Nickel

Benedetti-Pichler, 22

Bobtelsky and Welwart, 35, 36 Furman, 82

Llacer, Sozzi, and Benedetti-Pichler, 155 Steyermark, 223

Palladium

Kinnunen and Merikanto, 125 Konig, Crowell, and Benedetti-

Pichler, 135 Steyermark, 223 Platinum

Steyermark, 223 Potassium

Belcher and Robinson, 20 Bullock and Kirk, 42 Chapman, 46

Cimerman and Rzymowska, 5 3

Cimerman, Wenger, and Rzymowska, 58 Flaschka and Amin, 78

Hegedus and Dvorszky, 98 Herrmann, 102

143 Table of References

T A B L E 16 Potassium (Conf.)

Heyrovsky, 103

Kingsley and Schaffert, 123, 124 Klein and Jacobi, 128

Korenman, Sheyanova, and Glazu- nova, 136

Kreisky, 140 Lewis, 151

Robinson and Hauschildt, 191 Schuhknecht and Schinkel, 207 Steyermark, 223

Selenium

Alber and Harand, 2 Gould, 89

Kahane and Korach, 119 Kan, 120

Kondo, 134

Wernimont and Hopkinson, 245 Zabrodina and Bagreeva, 248 Silicon

Fennell and Webb, 73

Klimova and Bereznitskaya, 129, 130 Klimova, Korshun and Bereznitskaya,

131, 132

Kreshkov, Syavtsillo and Shemyaten- kova, 141

McHard, Servais and Clark, 162 Schoklitsch, 204

Thurnwald and Benedetti-Pichler, 233 Silver

Amin, 6

Emeléus and Haszeldine, 72 Flaschka, 75

Foulk and Bawden, 80 Furman, 82

Kuhn and Schretzmann, 143 Lambert and Walker, 145 Schulek, 208

Steyermark, 223 Sodium

Arnold and Pray, 9 Barber and Kolthoff, 13 Caley and Foulk, 44 Flaschka and Amin, 78

(Continued)

Sodium (Conf.)

Hegedus and Dvorszky, 98 Hegedus, Fukker, and Dvorszky, 99 Herrmann, 102

Holmes and Kirk, 109

Kingsley and Schaffert, 123, 124 Kreisky, 140

Schuhknecht and Schinkel, 207 Solomon, 220

Steyermark, 223 Strontium

Pungor and Hegedus, 186 Pungor and Thege, 187 Steyermark, 223

Strebinger and Mandl, 228 Zombory, 249

Thallium

Cimerman and Selzer, 55 Flaschka, 76

Thorium

Ishibashi and Higashi, 115

Venkateswarlu, Ramanthan, and Nara- yana Rao, 240

Tin

Furman, 82 Holtje, 110 Price, 185

Silvert and Kirner, 214 Uranium

Bobtelsky and Hapern, 27 Emeléus and Haszeldine, 72 Zinc

Anderson, 8

Cimerman and Selzer, 54 Cimerman and Wenger, 56, 57 Furman, 82

Hibbard, 104 Lamm, 146 Lang, 147 Martin, 159 Zirconium

Leonard, Sellers, and Swim, 149

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